The former Conservative defence secretary Liam Fox said that Nato was responsible for peace in Europe, not the EUGetty

Former British defence secretary Liam Fox tore into David Cameron's renegotiation efforts with Brussels, as he made a surprise speech at the launch of the new Grassroots Out (GO) campaign on 23 January. The senior Conservative MP accused his party's leader of taking the "political begging bowl" around the continent in a bid to get European leaders to back his plan to block EU migrants in the UK from accessing welfare payments for at least four years.

"I didn't give up my job as a family doctor to go to Westminster to see it play second fiddle to Brussels and the European Court," Fox told the 2,000 strong audience in Kettering. "When I gave up my medical career I didn't expect a British prime minister to have to take the political begging bowl around the capitals of Europe just to change our own benefit laws in our own country."

The former minister added: "It is time to look forward and outwards with hope and opportunism – we don't want to be 'little Europeans', but to embrace the wider world with all the opportunities that it offers. It is now time – time to take control of our own destiny."

The comments come after Cameron signaled a U-turn over his benefits proposal, which makes up one of his four major reforms. The prime minister said he was "open" to alternative methods to reduce net migration to the UK when he spoke in the Czech Republic on 22 January.

The Tory leader has faced opposition from the Visegrád Group (made up of the Czech Republic, Slovakia, Poland and Hungary) over the benefits plan. Bohuslav Sobotka, the Czech premier, has proposed a so-called "emergency break", which would see EU states apply to Brussels to close their borders when migration levels hit a certain threshold.

Elsewhere, Fox attacked pro-EU politicians over the claim that the 28-nation bloc has prevented conflicts across the continent. The former defence secretary argued that North Atlantic Treaty Organisation (Nato) should be credited for keeping the peace. The Tory MP spoke after Ukip leader Nigel Farage, who claimed "tens of millions" of people across Europe would be behind GO.

The group, which also has the backing of Labour MP Kate Hoey, Tory MP Peter Bone and DUP MP Sammy Wilson, is now the third Brexit campaign to launch ahead of the EU referendum, which will be held before the end of 2017. However, unlike Vote Leave and Leave.EU, GO will not compete for the Electoral Commission's official Brexit campaign nomination.

The Britain Stronger In Europe campaign have claimed GO's establishment is a "damning indictment" of Vote Leave and Leave.EU. "It shows how much the constant bickering and 'friendly fire' has distracted them from properly engaging in this important debate about Britain's future," said James McGrory, chief campaign spokesman for Stronger In.

The latest online opinion poll from Survation, of more than 1,000 people between 15-16 January, put "leave" four points ahead of "remain" (42% versus 38%, respectively).